This invention relates in general to respirators and in particular to a new and useful control device for respirators.
Lung machines for respirators are intended to make sure, in any event, that the user of the respirator, who is then always in a dangerous situation or one which is strenuous for him, is supplied with respiratory air. This must be ensured also in case the important pressure reducer, in which the bottle pressure is reduced, should fail.
From U.S. Pat. No. 3,957,044 a respirator is known which is supplied with compressed air or oxygen from a bottle. The equipment operates in two pressure stages, in which the last is the lung machine which sends the respiratory gas directly to the user. The first stage contains two pressure reducers connected in parallel, the operating pressure reducer and the reserve pressure reducer, in which the pressure of the respiratory gas is reduced to match the lung machine. The pressures behind the two pressure reducers differ insignificantly.
The operating pressure reducer reduces the bottle pressure to a medium pressure of about 6 bars. The latter is supplied via a medium pressure line to a lung machine valve connected to a mask. A check valve in the medium pressure line permits flow only from the operating pressure reducer to the lung machine.
The lung machine lets the gas flow to the user in unison with his breathing. Arranged parallel to the operating pressure reducer is the reserve pressure reducer, whose reserve medium pressure is adjusted to about 9 bars. The discharge of the reserve pressure reducer is connected, via a reserve line which contains a normally closed automatic shutoff valve, with the medium pressure line behind the check valve. The automatic shutoff valve is actuated pneumatically and for this purpose has a control piston provided with different piston surfaces. Its larger piston surface, acting in the closing direction, is pressurized by the medium pressure, derived between the pressure reducer and the check valve. The smaller piston surface, acting in the opening direction, is pressurized by the reserve medium pressure. The matching of the surfaces brings about the closing of the shutoff valve under normal conditions. If, however, upon failure of the operating pressure reducer, the medium pressure collapses, the then predominant reserve medium pressure opens the shutoff valve, and the gas flowing to the lung machine via the reserve line maintains the supply. At the same time a warning signal sounds with every respiration. In this state the check valve is necessary so that the reserve medium pressure cannot get to the larger piston surface in the return flow and cannot lead to reclosing of the shutoff valve or to its swinging.
When a minimum bottle pressure is not reached, the reserve line is connected by a pneumatic switching valve switched directly with the bottle pressure in any event, even if the operating pressure reducer should not be defective, so that a warning signal is produced.
This residual pressure warner is not part of the present problem, it is known in many variations.
For the problem at hand, this known safety connection with an additional complete pressure reducer and the check valve is not only very costly but involves considerable weight for the user, which he must drag along continuously just in case a failure should occur. Moreover, the reserve pressure reducer, which of course is a complicated device and as a rule remains unused in reserve, may itself easily fail in any emergency.